Dialing up the laser power

AUSTIN, Texas – Over the past 20 years, physicists have been steadily stepping up the power of lasers from
the previously impressive terawatt level to the recently realized petawatt level.
Now, researchers at the University of Texas are working toward building the first
exawatt laser, which will be the most powerful laser in the world.

“Every leap in power made by the laser community has led
to dramatic and unexpected applications,” said professor Todd Ditmire, who
heads up the Texas Petawatt project. “The leap in power by a factor of 1000
that an exawatt laser would provide will no doubt lead to new applications.”

Current research uses for the Texas Petawatt Laser include producing
thermonuclear fusion, a process that many engineers would like to harness for the
commercial generation of electricity. Other applications include the study of hot,
dense plasmas.

This shows the amplifier bay of the Texas Petawatt Laser. Images
courtesy of the Texas Petawatt project.
Reaching exawatt levels should push these studies to new extremes
and likely reveal new applications. So convinced are they about the coming applications
that Ditmire and colleagues have formed their own company, National Energetics,
to commercialize their work.

“An exawatt laser might be used to accelerate particles
to a very high energy. We might imagine accelerating electrons to energies of up
to one teraelectronvolt, which is 10 times higher than the energy produced by the
Stanford Linear Accelerator Center in California,” Ditmire said. “It
might also be used to create a small amount of matter in the lab that has a relativistic
temperature. Such temperatures are thought to exist near black holes and are very
exotic states of matter.”

Shown is the large silicate glass rod that is used in the amplifier chain.
While a number of petawatt lasers already exist around the world,
the Texas Petawatt Laser uses a new mixed glass approach to amplify pulses with
durations down to nearly 100 fs.

The method is based on chirped pulse amplification, which involves
stretching a femtosecond pulse to make it safe for amplification. After the pulse’s
energy is boosted, the pulse is recompressed in time to create a high-peak-power
pulse.

“We start with a very low energy femtosecond oscillator
to produce broadband pulses, which are stretched using diffraction gratings in order
to spread the colors of the pulse out in time,” Ditmire explained. “Then,
the pulse is amplified with nonlinear optical crystals followed by large mixed glass
amplifiers. Finally, the pulse transits two more gratings, which compress the colors
back to a pulse duration near that of the initial seed pulse.”

Pictured is a view down the axis of the large 31-cm glass disk amplifiers.
The Texas team hopes that, by developing new kinds of glass for
use in the mixed glass amplifier, it will be able to make a laser with energies
exceeding 100,000 joules and a pulse duration of less than 100 fs.

“The next steps involve working with German glassmaker Schott
Glass to develop the new kinds of laser glass we will need for an exawatt laser,”
Ditmire said. “In parallel, we are commercializing the mixed glass architecture.”